1. Field of the Invention
The present invention relates to bearing assemblies, and, more particularly, to roller bearing assemblies having a pin carrying a roller bearing.
2. Description of the Related Art
A roller bearing assembly typically includes a roller bearing rotatably carried by a pin. Such bearings are suitable in many applications. One such application is for use as part of a cam follower which rides against a cam lobe of a camshaft in an internal combustion (IC) engine. To better distribute mechanical load and provide proper lubrication through the formation of an oil film, it is desirable to maintain a close clearance between the outside diameter of the pin and the bore of the roller bearing. However, to maintain adequate oil flow and because of thermal expansion that occurs after start-up, it is also necessary to provide enough clearance to accommodate such expansion. Conflicting design objectives are thus present.
For certain applications such as the camshaft and cam follower application identified above, loads applied to the pin carrying the roller bearing are primarily of a unidirectional nature. The mechanical load applied to the pin during engine rest squeezes the oil from the area between the pin and inside diameter of the roller bearing. At start-up, the roller bearing must reach a certain rotational speed to establish hydrodynamic lubrication.
What is needed in the art is a roller bearing assembly which accommodates thermal expansion, provides a close clearance between the pin and roller bearing in the area of mechanical loading, and develops an adequate minimum oil film thickness at a lower rotational speed.